Impact craters form when meteorites strike the solid surface of a planetary body. Here the lunar crater Euler shows land forms typical of fresh craters the size of the largest in the Gangis Chasma image. The rim of the crater is sharp, and the crater is surrounded by a hummocky halo of ejecta, rock thrown out of the crater on impact. The interior walls of the crater are steep, and often modified by landslides, yielding slump blocks along the walls. The walls are often modified further by rockfalls or other mass wasting, producing talus slopes and cones. In the center of the crater bowl is the central peak, which is rock from below the impact site that "bounces" (rebounds) back up after the impact. Craters of this size and larger commonly have smooth floors, which may be impact melt (rock melted by the impact), debris aprons from the landslides that formed slump blocks on the walls, or lava lakes.